The steam turbine has until recently been the first choice for very large
power marine propulsion units. Its advantages of little or no vibration, low
weight, minimal space requirements and low maintenance costs are
considerable. Furthermore a turbine can be provided for any power
rating likely to be required for marine propulsion. However, the higher
specific fuel consumption when compared with a diesel engine offsets
these advantages, although refinements such as reheat have narrowed
the gap.

The steam turbine requires a considerable period for warming-through
prior to any manoeuvring taking place. The high-speed operation of the
turbine and its simply supported rotor also require great care during
manoeuvring operations.

Warming-through a steam turbine

First open all the turbine-casing and main steam-line drain valves and
ensure that all the steam control valves at the manoeuvring station and
around the turbine are closed. All bled steam-line drain valves should be
opened. Start the lubricating oil pump and see that the oil is flowing
freely to each bearing and gear sprayer, venting off air if necessary and
check that the gravity tank is overflowing.

Obtain clearance from the bridge to turn the shaft. Engage the
turning gear and rotate the turbines in each direction.

Start the sea water circulating pump for the main condenser. Then
start the condensate extraction pump with the air ejector recirculation
valve wide open.

Fig: Energy conversion in a steam turbine

Open the manoeuvring valve bypass or 'warming
through' valve, if fitted. This allows a small quantity of steam to pass
through the turbine and heat it. Raising a small vacuum in the
condenser will assist this warming through. The turbines should be
continuously turned with the turning gear until a temperature of about
75°C is reached at the LP turbine inlet after about one hour. The
expansion arrangements on the turbine to allow freedom of movement
should be checked.

Gland sealing steam should now be partially opened up and the
vacuum increased. The turning gear should now be disengaged.

Short blasts of steam are now admitted to the turbine through the
main valve to spin the propeller about one revolution. This should be
repeated about every three to five minutes for a period of 15 to 30
minutes. The vacuum can now be raised to its operational value and also
the gland steam pressure. The turbines are now ready for use.
While waiting for the first movements from the bridge, and between
movements, the turbine must be turned ahead once every five minutes
by steam blasts. If there is any delay gland steam and the vacuum should
be reduced.

Manoeuvring

Once warmed through, the turbine rotor must not remain stationary
more than a few minutes at a time because the rotor could sag or distort,
which would lead to failure, if not regularly rotated.

Astern operation involves admitting steam to the astern turbines.
Where any considerable period of astern running occurs turbine
temperatures, noise levels, bearings, etc., must be closely observed. The
turbine manufacturer may set a time limit of about 30 minutes on
continuous running astern.

Emergency astern operation

If, when travelling at full speed ahead, an order for an emergency stop
or astern movement is required then safe operating procedures must be
ignored.

Ahead steam is shut off, probably by the use of an emergency trip, and
the astern steam valve is partly opened to admit a gradually increasing
amount of steam. The turbine can thus be brought quickly to a stopped
condition and if required can then be operated astern.

The stopping of the turbine or its astern operation will occur about 10
to 15 minutes before a similar state will occur for the ship. The use of
emergency procedures can lead to serious damage in the turbine,
gearbox or boilers.

Full away

Manoeuvring revolutions are usually about 80% of the full away or full
speed condition. Once the full away command is received the turbine
can gradually be brought up to full power operation, a process taking
one to two hours. This will also involve bringing into use turboalternators
which use steam removed or 'bled' at some stage from the
main turbines.

Checks should be made on expansion arrangements, drains should be
checked to be closed, the condensate recircuiation valve after the air
ejector should be closed, and the astern steam valves tightly closed,

Port arrival

Prior to arriving at a port the bridge should provide one to two hours'
notice to enable the turbines to be brought down to manoeuvring
revolutions. A diesel alternator will have to be started, the turboalternator
shut down, and all the full away procedure done in reverse
order.

Steam for cargo discharge or ballast water operation

Certain ships such as large crude oil and product tankers as well as ships for the need for large ballast pump may use steam-driven turbines to drive the cargo and ballast pumps.

In these ships, extra boilers are operated to drive the cargo pump steam turbines as well as for inert gas generation. Cargo pump driven steam turbines are highly inefficient (with an overall efficiency of about 10-15%) and care should be exercised in their usage level.

During cargo discharging operations, vacuum should be maintained properly in the vacuum condenser. This will ensure better work transfer across the steam turbine thereby increasing output at the same boiler load. During cargo discharging operation, better coordination and planning must be maintained with the terminal personnel (loading master, terminal representative(s)) as also on board with deck and engine department so as to reduce idle firing period of main boilers; reducing unnecessary / prolonged cargo oil pumps’ warm up period, idle running of inert gas plant etc.

The steam turbine is a device for obtaining mechanical work from the
energy stored in steam. There are two main types of turbine, the 'impulse' and the 'reaction'.
The names refer to the type of force which acts on the blades to turn the
turbine wheel. More.....

A turbine protection system is provided with all installations to prevent damage resulting from an internal turbine fault or the malfunction of
some associated equipment. Arrangements are made in the system to
shut the turbine down using an emergency stop and solenoid valve. More.....

Helical gears have been used for many years
and remain a part of most systems of gearing. Epicyclic gears with their
compact, lightweight, construction are being increasingly used in marine
transmissions. More.....

Steam-to-steam generators produce low-pressure saturated steam for domestic and other services. They are used in conjunction with
watertube boilers to provide a secondary steam circuit which avoids any
possible contamination of the primary-circuit feedwater. . More.....

Compounding is the splitting up, into two or more stages, of the steam pressure or velocity change through a turbine. Pressure compounding of an impulse turbine is the use of a number of stages of nozzle and blade to reduce progressively the steam pressure.. More.....

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